This invention relates to an improved gypsum wallboard faced with fiber mat. More particularly, the present invention relates to a gypsum wallboard covered with a glass fiber mat (preferably a coated glass mat) on one face, and paper on the opposite face. The wallboard of the present invention is particularly advantageous for use in applications where a face of the wallboard will confront a confined area in which mold propagation may be a concern, such as, e.g., certain interior wall cavities. Still other applications will become apparent from the detailed description of the invention.
Panels of gypsum wallboard having a core of set gypsum sandwiched between two sheets of facing paper have long been used as structural members in the fabrication of buildings. Such panels are typically used to form the partitions or walls of rooms, elevator shafts, stairwells, ceilings and the like. Although paper is a relatively inexpensive facing material and easily used in the process of manufacturing wallboard, it is has disadvantages, particularly with regard to moisture-resistance. Moisture can have deleterious effects upon wallboard. In addition to degrading strength and other structural properties, moisture (in combination with other factors) can encourage the growth of fungi (including, e.g., mold). The problem can (under certain circumstances) be particularly acute with regard to certain spaces that, upon installation of the wallboard, are enclosed and inaccessible.
An example of this problem can occur with regard to interior walls. As is known in the art, interior walls are often formed by erecting a supporting structure (which may include wood or metal studs), and then fastening gypsum wallboard to that structure from floor to ceiling. A confined cavity is thereby formed within the wall. That cavity may be empty, or it may contain insulation, wiring, piping, etc. Once the wall is completed, however, that cavity is generally inaccessible without removing the wallboard, which must then be replaced. Even though inaccessible, a wall cavity is often susceptible to moisture penetration and collection. This may occur through leakage of pipes within the cavity, by condensation, by leaking of a roof, flooding, etc. If the wallboard is not resistant to water penetration, the facing and gypsum core may absorb water. Because wall cavities are typically not ventilated, the water may tend to remain, and fungal growth can occur.
As an alternative to paper facing, gypsum wallboard can also be manufactured with a fibrous mat (such as glass fiber) as a facing material. Examples of such wallboards include that described in, e.g., U.S. Pat. No. 3,993,822. In addition to improved water a resistance, fibrous matting often provides significant improvements in strength and other structural attributes. Although fibrous matting is a more advantageous facing material than paper in many respects, it may be less desirable than paper in other respects. For example, fibrous mat can be more expensive than paper. Glass or other fiber matting also provides a less desirable wall surface in some applications. Interior walls, for example, are often finished with paint or wall paper. Paper facing offers a smoother surface for painting or wall papering than is offered by fibrous mat facing.
It is also known in the art to manufacture gypsum wallboards for interior use having shaped regions near the edges. This shaped region can form a bevel, a taper, a rounded edge, or other desired shape. This shaping is often formed on the interior face (i.e., the face exposed to a room interior after installation). A cross section of such an existing wallboard is shown in FIG. 1A; various angles, thicknesses and other dimensions are exaggerated for clarity. Typically, the wallboard has a first face covered with a smooth paper facing material wrapped around the gypsum core. A second face is likewise covered with a paper facing material overlaying the gypsum core. The facing material from the first face is typically wrapped around the edges of the board and is overlapped at its margins by small portions of the facing material on the second face. The shaped regions can allow a small depression to be formed along the joints of adjoining wallboards. Specifically, the first faces of adjoining wallboards are oriented so as to confront the interior of a room, with their edges touching (or very close together). Joint tape, drywall mud, etc. can be placed into the depression to provide a finished wall that is generally flat (e.g., without ridges along the wallboard joints) and ready for painting or wallpapering. FIG. 1A also shows, on the left hand side of the figure, additional examples of shapes that may be formed.
Although interior wallboards with shaped regions on an interior face are used in applications which might benefit from the advantages of both fiber matting and paper facing materials, combining such materials in a single board for such an application presents potential problems, and has not been described in the prior art. Because dissimilar facing materials would generally create different stresses during fabrication of the wallboard, warpage would be expected to occur. Moreover, conventional manufacturing methods require that the shaped regions be formed on the bottom surface of a horizontal wallboard as it progresses down a production line during fabrication. FIG. 1B is a schematic cross section of a prior art wallboard during manufacture. The center would typically be horizontal, with two small shaping forms attached to, and running the length of, the conveyor. The upper surface of the forming wallboard would typically be flat. This arrangement, however, requires that the facing material on the bottom (conveyor) side be used to wrap around the edges of the wallboard during fabrication. In order to manufacture an interior wallboard using conventional methods, and having shaped regions on the paper-covered face and a mat-covering on the other face, it would be necessary to place the paper web on the bottom (conveyor) surface and the mat web on the top surface. However, the paper web would then be wrapped around the edges of the fabricated wallboard. In this configuration, and upon installation of a wallboard in a wall, the paper facing material would be exposed to the confined interior wall cavity. As set forth above, paper can be less water-resistant than fibrous matting. Moreover, the joints between adjacent wallboards are generally not sealed on the wall cavity side. A paper-wrapped edge could thus provide a path for moisture to infiltrate the wallboard, and at least partially defeat the benefits of the mat facing material.
According to the present invention, a gypsum wallboard has a paper-covered first face with shaped regions near the edges, and a second face covered with a water-resistant facing material, preferably a fibrous mat material, and more preferably a coated fibrous mat material. The paper-covered first face presents a good surface for painting or wallpapering. The second face, because of its preferred coated mat facing material, is resistant to water infiltration. The mat material covering the second face wraps around the edges of the wallboard. Preferably, the mat material terminates on the shaped regions of the first face. The paper facing material is glued to the mat along an overlap of the two facing materials, preferably on the shaped regions of the first face.
According to another aspect of the invention, a process for fabricating a wallboard with shaped regions is provided. A bottom web of facing material is continuously fed. Onto the bottom web is deposited a gypsum slurry. Lateral portions of the bottom web are wrapped around the edge of the forming wallboard and overlap side portions of the upper slurry surface along its margins. A top web of continuously fed facing material is applied to the upper surface of the slurry, and is glued along regions of overlap of the two facing materials A series of shims located along the lateral margins of the upper surface of the forming wallboard form shaped regions in those margins. In this manner, it is thereby possible to continuously form wallboard having shaped regions in a first face, with the facing material of a second face extending around the wallboard edges.